1. Field of the Invention
The present invention relates to motorized switches.
2. Description of Related Art
U.S. Pat. No. 2,280,898 discloses a capacitor tripping device for circuit breakers. U.S. Pat. No. 3,064,163 discloses a capacitor trip arrangement for an electric circuit breaker. U.S. Pat. No. 3,211,958 discloses a capacitor tripping device for circuit breakers. U.S. Pat. No. 6,842,322 discloses an electronic trip device comprising a capacitor for supply of a trip coil. U.S. Pat. No. 7,432,787 discloses a motorized loadbreak switch control system and method. Each of these patents is incorporated by reference in its entirety.
High voltage switching mechanisms, such as medium voltage switchgears, currently use expensive, large-footprint contactors. Although it would be advantageous for various reasons to use motorized switches instead of contactors, unlike contactors, however, motorized switches retain their open or dosed state upon loss of power. In contactors, a magnetic coil doses the contacts once it is energized, and a spring mechanism opens the contacts once power is removed (or is lost) to the coil, thus ensuring contactors always open upon power loss.
This limitation in motorized switches renders them unusable in applications where it is desired that the switching mechanism open when power is removed. An example where such a feature is required is in some distribution-class equipment such as medium voltage switchgears or variable frequency drives where the switching device (most commonly a contactor) is used to connect the power source to the load.
In these applications, if the power supply is removed, and the switching device remains closed, once power is restored, the bad will be connected directly to the power source without any operator control, which is highly undesirable.
Although there are many designs for motorized switches that are well known in the art, considerable shortcomings remain. What is needed is a motorized switch that will automatically switch to the “open” position upon loss of power.